babelfish for postgresql 分析--babelfishpg_tds--doing

babelfishpg_tds插件支持了TDS 协议扩展，实现 TDS 客户端-服务器协议

先看插件加载时的函数

c 复制代码

void
_PG_init(void)
{
	//是否已加载
	static bool inited = false;
	if (inited)
		return;
	//tds插件必须在shared_preload_libraries中，在数据库启动时即加载
	if (!process_shared_preload_libraries_in_progress)
		ereport(ERROR, (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
						errmsg("babelfishpg_tds must be loaded via shared_preload_libraries")));
	//初始化guc参数，见下表
	TdsDefineGucs();
	//创建了一个插件ptr，暂时未看到具体使用
	tds_instr_plugin_ptr = (TdsInstrPlugin **) find_rendezvous_variable("TdsInstrPlugin");
	//初始化端口监听等，在postgresql中实现tds协议的核心
	pe_init();
	//内核中新增了relname_lookup_hook hook，返回保存在tvp_lookup_list中的relid
	prev_relname_lookup_hook = relname_lookup_hook;
	relname_lookup_hook = tvp_lookup;

	/* Shmem hooks */
	//共享内存中创建TdsStatus，保存每个连接tds的状况
	next_shmem_startup_hook = shmem_startup_hook;
	shmem_startup_hook = tds_status_shmem_startup;

	prev_shmem_request_hook = shmem_request_hook;
	shmem_request_hook = tds_shmem_request;

	/* Install our object_access_hook into the chain */
	next_object_access_hook = object_access_hook;
	//object_access_hook，主要检查是否有权限drop user
	object_access_hook = babelfish_object_access;

	/* Install our process utility hook into the chain */
	next_ProcessUtility = ProcessUtility_hook;
	//Utility hook，用于在执行ddl前做额外的权限检查，检查的语句有DropRoleStmt，T_RenameStmt，T_DropdbStmt，T_AlterRoleStmt，T_AlterRoleSetStmt，T_GrantRoleStmt，在执行完检查后执行正常的ProcessUtility，通过调用next_ProcessUtility 
	ProcessUtility_hook = tdsutils_ProcessUtility;

	inited = true;
}

新增guc参数

参数	GucContext	说明	默认值
babelfishpg_tds.port	PGC_POSTMASTER(数据库启动时设置)	tds监听的端口	1433
babelfishpg_tds.listen_addresses	PGC_POSTMASTER(数据库启动时设置)	tds监听的ip	*
babelfishpg_tds.unix_socket_directories	PGC_POSTMASTER(数据库启动时设置)	TDS server unix socket directories	NULL
babelfishpg_tds.unix_socket_permissions	PGC_POSTMASTER(数据库启动时设置)	TDS server unix socket permissions	0777
babelfishpg_tds.unix_socket_group	PGC_POSTMASTER	TDS server unix socket group.	NULL
babelfishpg_tds.default_server_name	PGC_SIGHUP(数据库启动时设置或者reload触发中断设置)	默认server name	Microsoft SQL Server
babelfishpg_tds.product_version	PGC_USERSET(用户可修改)	Product Version returned by Babelfish	default
babelfishpg_tds.tds_default_numeric_precision	PGC_SIGHUP	默认numeric精度	38
babelfishpg_tds.tds_default_numeric_scale	PGC_SIGHUP	默认numeric范围	8
babelfishpg_tds.tds_ssl_encrypt	PGC_SIGHUP	ssl加密开关	false
babelfishpg_tds.tds_default_protocol_version	PGC_SIGHUP	tds协议版本	TDS_DEFAULT_VERSION
babelfishpg_tds.tds_ssl_max_protocol_version	PGC_SIGHUP	ssl协议最大版本	PG_TLS1_2_VERSION
babelfishpg_tds.tds_ssl_min_protocol_version	PGC_SIGHUP	ssl协议最小版本	PG_TLS1_VERSION
babelfishpg_tds.tds_default_packet_size	PGC_SIGHUP	发送的packet大小	4096
babelfishpg_tds.tds_debug_log_level	PGC_SIGHUP	日志级别	1
enable_drop_babelfish_role	PGC_USERSET	是否可以删除一个babelfish role	false
babelfishpg_tds.trigger_fault_enabled	PGC_SUSET	Enable fault injection triggers	true